Certain types of audio telephony are susceptible to degradations in voice quality. For example, cellular telecommunications is notorious for marginal-to-poor call quality at certain times of the day and year, and in certain geographic areas where coverage is a problem.
In one sense, the problem is particularly annoying when one of the communication paths between two call participants is afflicted with poor call quality at a particular moment, while the other path still has acceptable quality. This occurs frequently in cellular telecommunications, in which the uplink path (i.e., from the phone to the radio base station) and the downlink path (i.e., from the radio base station to the phone) are often RF-engineered differently from each other. A consequence of this difference in the engineering between the two transmission links is that the call quality might also be asymmetrical at times during a call.
Where asymmetry in the call quality is present, for example, a first call party on a cell phone call might continue to speak for several seconds before realizing that some or all of what he was just saying was not clearly heard by the second call party. The first party then has to figure out what was missed by the second party and repeat some or all of what was said. This is a situation that virtually every cell phone user has experienced at least once, and one that has often resulted in frustration and lost time.
Various approaches in the prior art have been devised to address the problem of asymmetry between call participants. One such approach involves the use of military communication protocol, in which explicit repetitions and special words are used throughout a conversation. The advantage of this approach is that it can be used by the call participants irrespective of the underlying nature of the communication system (e.g., Public Switched Telephone Network [PSTN], Voice over Internet Protocol [VoIP], cellular, etc.). The disadvantage is that most call participants would find the use of repetitions and special words to be cumbersome.
In another approach, an evaluation device is installed inline of the handset at one of two communication points. The device determines the Perceptual Evaluation of Speech Quality (PESQ) Mean Opinion Score (MOS) by sending a known voice stream in each of the two directions of communication. SAGE Electronics, for example, sells such a device. Disadvantageously, however, PESQ is an obtrusive testing method in the sense that the voice channel cannot be used for speech communications during the use of the evaluation equipment.
Yet another type of approach involves the use of ITU standards P.562 and P.563, which deal with measuring and analyzing voice quality. They specify software to analyze audio from live calls and to give the audio an MOS score that predicts how a panel of test experts would rate a call. Methods using these standards would be unobtrusive, in that they would operate on live voice waveforms and would not alter speech communications quality. Disadvantageously, however, these standards appear to be too complex to justify their implementation in mass-produced endpoints.
Elements of a possible approach exist in the information sent by the Real-time Transport Control Protocol (RTCP), which is used to report reception quality to the remote communication endpoint in VoIP applications. The advantage of an approach if based on RTCP data is that it would rely on a standard protocol. RTCP data, however, is not used to provide an explicit feedback of the quality to the call participants themselves, in part because RTCP was designed to feed a system (e.g., an endpoint) which eventually could adjust a communication codec so as to achieve better call quality. Even that objective, however, does not yet appear to have been met. And in any event, the RTCP data might not be sufficient to prove that the adjusted call quality is adequate.
What is needed is a technique, without some of the disadvantages in the prior art, to provide feedback to a first call participant about whether he is being adequately heard by a second call participant.